It is known that conventional electric rolling doors are essentially designed to include a motor-driven barrel, which is controlled to have the curtain of slats rolled up and wound around the barrel for opening the door during forward rotation; or to have the curtain pushed out for closing the door during reverse rotation. After the door has been opened or closed to its upper or lower dead position, the input current to the motor is cut off, a cam shaft which is acted upon by a spring pushes the brake shoes of a drum brake device open to have the motor shaft braked such that the door is held at its opened or closed condition. Under normal power supply, there are no significant disadvantages with the operation of conventional electric rolling doors. In case of power failure, however, when one wants to open the curtain after it has been closed, because of the inherent structure, the operator has to pull the brake release cable to pull the cam shaft of the braking device to have the brake released with one hand, and to pull the chain to rotate the rotating shaft so as to cause barrels to rotate and have the curtain rolled up with the other hand. Therefore, conventional electric rolling doors must be operated by using both hands under no power supply, which is rather undesirable such that improvements have yet to be made.